Drive for precision oscillations

ABSTRACT

A drive device for generating oscillations, especially for the blade of a microtome, with a power generator and a power transmission element, which with the power generator is movable in a predetermined oscillation direction (S), whereby the power generator includes a combination of a permanent magnet part and a coil part, whereof one part is fixed stationary on a holder and the other part on the power transmission element, respectively, and the power transmission element is formed by a vibrational arm, which is fixed at one end to the holder and which is elastically bendable in the oscillation direction and still in all other directions.

FIELD OF THE INVENTION

The invention relates to a drive device for generating vibrations, inparticular for precision tools and manipulators, such as for example adrive for the cutting tool of a microtome, and a microtome that isequipped with such a drive device.

BACKGROUND

Conventional microtomes for producing thin tissue sections are as a ruleequipped with an eccentric drive, which sets a blade in a horizontaloscillation. By means of a feed device, the oscillating blade is passedthrough an object to be processed, fresh tissue for example, so that thedesired section of the object is severed. The use of eccentric drives isbound up with a number of drawbacks. The oscillation frequency of theblade is limited, because with the eccentric drive the masses of a knifeholder and guides also have to be accelerated. Furthermore, theoscillation amplitude of the blade is also restricted by the eccentricitself to around 1 mm as a rule. An essential drawback in the productionof precision sections of biological materials is caused by the formationof vertical movements (vertical beats), which diverge from thehorizontal oscillation direction of the blade. The eccentric drivegenerates a vertical beat at its reversal points. Furthermore, thetendency towards vertical oscillation increases at higher oscillationfrequencies, at which the effective forces increase. As a result of thevertical oscillations, the tissue to be processed is separated not onlyin the feed direction. Cells in the tissue surface are also damaged.This makes the subsequent examination of the tissue section moredifficult.

In a modified design of a microtome, such as is commercially availablefor example under the name “Vibracut 3”, manufacturer: FTBFeinwerktechnik, the knife holder is caused to oscillate with a movinglift magnet. This form of drive is disadvantageous, since the vibrationfrequency of the blade is tied to the resonance frequency of the knifeholder. Furthermore, it is in turn not possible to rule out verticaloscillations to the extent required for precision applications,especially in microbiology and neurology.

The stated problems with the vibrational drive of a microtome blade alsoarise with other precision tools and manipulators with which a linearoscillatory motion in a predetermined oscillation direction is desired,whilst in all other directions no deflection movements take place. Thisconcerns, for example, tools for the processing of micro-systems ormicro-surgical instruments.

It would accordingly be advantageous to provide an improved drive devicefor generating vibrations, with which the drawbacks of the conventionaldrives for precision tools or manipulators are overcome and which inparticular enables a generation of vibrations in a predeterminedoscillation direction with an adjustable oscillation frequency andoscillation amplitude and without lateral deflections. It would also beadvantageous to provide an improved microtome, with which the thicknessof tissue sections can be reduced and the damage to tissue parts outsidein the sectioning direction can be reduced.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a drive device (precisionvibrational drive) in particular is created, which contains as a powergenerator a combination of a magnet with a permanent magnetic field anda magnet with a periodically variable magnetic field, with which a powertransmission element can be set into an oscillatory motion relative to astationary holder according to a predetermined oscillation direction.The power transmission element is formed in particular by a vibrationalarm fitted on the holder, which vibrational arm comprises at least oneplane-shaped strip of elastic material which is flexible in theoscillation direction and inflexible or stiffened in all otherdirections. The vibrational arm is preferably formed as a U-section. Theopen end of the U-section is fixed to the holder and the closed end ofthe U-section is elastically bendable in the section plane correspondingto the oscillation direction. According to a preferred embodiment of theinvention, the magnet with the permanent magnetic field is a bell-shapedmagnet and the magnet with the variable magnetic field is a plunger coilwhich is arranged in the bell-shaped magnet. The plunger coil is fixedat or near to the closed free end of the U-section of the powertransmission element and is connected electrically to an oscillationgenerator.

According to a further aspect of the invention, the precisionvibrational drive is driven in such a way that a forced oscillation isimparted to the power transmission element. The frequency and amplitudeof the forced oscillation can be adjusted according to the desiredmotion characteristics of the tool or manipulator to be operated.According to a preferred embodiment, a control circuit is implementedfor the frequency and amplitude adjustment using a bending sensor on thepower transmission element.

According to a still further aspect of the invention, a microtome isdescribed which is equipped with the aforementioned drive device. Thepower transmission element serves as a support of a microtome blade. Thestationary holder of the power generator or the power transmissionelement is fitted on a precision feed in the form of a linear table.

The invention has the following advantages. The drive device accordingto the invention delivers an oscillatory motion in a fixed oscillationdirection without lateral deflections, whereby the power transmissionelement is tied to the oscillation direction without mechanical guidessolely by means of its shape, in particular its sectional shape. Theoscillation frequency and amplitude are variable and adjustableindependently of one another. The microtome according to the inventionis distinguished by a greatly reduced vertical stroke. It is thuspossible to produce tissue sections with minimum damage to the surface.The drive device according to the invention has an extended area ofapplication also outside the microtome application.

BRIEF SUMMARY OF THE DRAWINGS

Further advantages and details of the invention will become apparentfrom the description of the appended drawings.

They show:

FIG. 1: a sectional view of an embodiment of the drive device accordingto the invention,

FIGS. 2 a & b: details of the power generator of the drive deviceaccording to FIG. 1,

FIG. 3: an outline diagram of a microtome according to the invention,and

FIGS. 4 a & b: graphical representations to characterize the oscillatorymotion of a blade of a microtome according to the invention.

DETAILED DESCRIPTION

The invention is described in the following by reference to a drivedevice for a microtome with given oscillation parameters of the blade.The invention, however, is restricted neither to the microtomeapplication nor to the oscillation parameters given by way of example.

Drive device 100 according to the invention comprises, according to thediagrammatic sectional view in FIG. 1, a power generator 10 and a powertransmission element 20, which is movable in a predetermined oscillationdirection (arrow S). The power generator comprises a permanent magnetpart and a coil part. The permanent magnet part is formed by thebell-shaped magnet fitted stationary on a holder 30, the details ofwhich bell-shaped magnet are explained by reference to FIGS. 2 a & b.The coil part is a plunger coil 12, which projects into bell-shapedmagnet 11. Plunger coil 12 is fixed to power transmission element 20.

Power transmission element 20 is formed by a vibrational arm 21, whichis fixed at one end to holder 30 and is freely mobile at opposite end22. Vibrational arm 21 is a U-profiled strip of a flat elastic material.This adjusts the mobility of free end 22 to bending in oscillationdirection S. In all other directions diverging from oscillationdirection S (in the drawing plane), vibrational arm 21 is a rigidstructure immobile relative to holder 30. At free end 22 or close to thelatter, plunger coil 12 is fixed with a fixing flange 23 to vibrationalarm 21. Bell-shaped magnet 11 in the U-section and plunger coil 12 areposition such that they are movable relative to one another inoscillation direction S. Generally, power transmission element 20 isdesigned as a support for a tool to be moved periodically or amanipulator or a tool holder. For this purpose, it has holding elements(not shown) on free end 22, depending on the application.

For use in a microtome, the drive device according to the inventionessentially has dimensions shown in FIG. 1 (scale 1:1). The vibrationalarm is made for example of aluminum sheet with a width of around 40 mmand a thickness of around 1 to 2 mm. The length of the vibrational armis selected according to the application. With a length of around 10 cm,the natural frequency of represented vibrational arm 21 with a U-sectionamounts to around 80 Hz. If, depending on the application, larger orsmaller frequency ranges (e.g. at around 10 Hz) are required, thevibrational arm should be designed accordingly with a smaller or greaterlength.

The parts of the drive device can be modified according to differentembodiments. In the case of the power generator, it is possible to fixthe coil part stationary on the holder and the permanent magnet part onthe power transmission element. Furthermore, it is possible to use, as apermanent magnet part, a differently formed permanent magnet or also acoil which is driven with a constant excitation current. Finally, apiezo drive could also be used alternatively as a power generator. Thepower transmission element may also be formed by a single strip-shapedsheet (see FIG. 2 b, which is flexible only at right angles to the sheetplane and otherwise rigid, or a complex profiled structure with only oneflexural degree of freedom.

Reference numeral 24 relates to a piezo bending element, which if needbe is fitted as a sensor on vibrational arm 21. The current oscillationamplitude of vibrational arm 21 can be detected with piezo bendingelement 24.

FIG. 2 shows details of power generator 10 in the disassembled (FIG. 2a) and assembled (FIG. 2 b) state. Bell-shaped magnet 11 is made ofhighly permanent material (e.g. of neodymium, B=1.17 T). The structureof the bell-shaped magnet preferably corresponds to the structure of abell-shaped magnet known per se, such as is used in loud speakers.Plunger coil 12 comprises a coil holder 13, coil winding 14 and a coilflange 15. Fixing flane 23, to which plunger coil 12 is fixed (e.g.glued) with coil flange 15, is fitted to vibrational arm 21 of the powertransmission element.

Plunger coil 12 is connected electrically to a supply device. Thiscontains an adjustable oscillation generator and a power amplifier(power e.g. 25 W). The oscillation generator is designed to generateelectrical oscillations in a frequency range from 30 to 130 Hz. Throughthe power of the power amplifier, the oscillation amplitude ofvibrational arm 21 can be adjusted continuously in the range from 0 to1.5 mm. A particular advantage of the invention consists in theadjustment of forced oscillations of the power transmission element. Inthe presence of excitation at a frequency, selected according toapplication, which is different from the natural frequency of the powertransmission element (with the respective tool or manipulator), itsoscillation frequency and amplitude can be freely adjusted.

According to a preferred embodiment of the invention, a control circuitis arranged for the adjustment of the oscillation amplitude and/orfrequency. The piezo bending element 24 on vibrational arm 21 is used asa sensor. Piezo bending element 24 is connected electrically to thesupply device. Depending on the current oscillation amplitude ofvibrational arm 21, the parameters of the supply device are changed forthe adjustment of a certain target value.

FIG. 3 illustrates in a diagrammatic side view a microtome 200 accordingto the invention, which is equipped with drive device 100 describedabove. Drive device 100 is constructed in accordance with the embodimentillustrated in FIGS. 1 and 2. In particular, vibrational arm 21 withfixing flange 23, plunger coil 12, permanent magnet 11 (dashed) andholder 30 are illustrated in FIG. 3. A tool 40 is fixed to free end 22of vibrational arm 21. Tool 40 comprises a vibrating fork 41, whichforms an extension arm for the blade. Knife holder 42 with blade 43 isfitted at the end of the extension arm. Knife holder 42 is fitted in aswivelling manner relative to vibrating fork 41. With drive device 100,horizontally aligned blade 43 is mobile in an oscillating manner in theoscillation direction at right angles to the drawing plane.

Furthermore, microtome 200 comprises a feed device 50 and a dissectingarea 60, which are accommodated on a lifting table 70. Feed device 50includes a linear table 51 known per se, which is driven by a spindle,gearing 52 and a d.c. motor 53. The d.c. motor is equipped with a d.c.tacho unit 54. A speed control is not required due to the provision of alarge gear reduction of around 200:1. The d.c. tacho unit generates adirect voltage which is proportional to the rate of feed and isdisplayed for example by a digital voltameter.

Dissection area 60 comprises a dissection tank 61, in which the objectto be processed, a biological tissue for example, is accommodated. Inplace of tank 61, any other form of specimen holder may also be provided(e.g. a platform or a clamping support). With an adjustment device 71 onlifting table 70, the height of blade 43 is adjusted relative todissection tank 61. For a rough adjustment, dissection area 60 may alsobe displaceable relative to lifting table 70. Adjustment device 71 is,for example, a micrometer screw. A graduation mark corresponds to 1 μmin the example shown.

To use microtome 200, a specimen is positioned in dissection tank 61.Blade 43 is returned to a starting point by feed device 50. The desiredheight of the blade is then adjusted with adjustment device 71. Drivedevice 100 is actuated, so that blade 43 performs horizontaloscillations. Simultaneously, oscillating blade 43 is driven by feeddevice 50 through the specimen, so that a section of the specimen islifted off and lies on blade 43.

Any suitable cutting tool, for example a razor blade, can be used asblade 43. To make optimum use of the oscillation capacity of the drivedevice according to the invention, which is essentially free fromvertical strokes, a blade made of an inflexible material, for example aceramic knife, is however preferred.

An important advantage of the invention, i.e. the considerable reductionin the vertical beat of the blade, is illustrated in FIGS. 4 a & b. Witha contactless inductive path sensor (e.g. sensor system IS 115, firmMicro-Epsilon), the vertical vibrations of the blade of a conventionalmicrotome (with eccentric drive, FIG. 4 a) and a microtome according tothe invention (FIG. 4 b) are recorded as a function of time. Thegraphical representations show a vertical beat of around 24 μm for theconventional microtome. The vertical beat of the blade with themicrotome according to the invention is 5 to 2 μm in the frequency rangefrom 30 to 130 Hz with amplitude of 1 mm.

In alternative applications, the drive device according to the inventionis used for the actuation of tools or manipulators for microsystemtechnology or of microsurgical tools or instruments. Several drivedevices can also be combined with one another, in that the holder of afirst drive device is itself caused to oscillate with another drivedevice in order to generate variable oscillation directions or periodicmovements of the tool or manipulator along predetermined curved paths.

1. A vibrational device for a tool or a manipulator comprising: a powertransmission element which forms a support for the tool or themanipulator, a power generator comprising a permanent magnet part and acoil part, wherein one of the parts is fixed on a holder and another ofthe parts is fixed on the power transmission element, and a bendingsensor for detecting oscillation amplitude of the power transmissionelement on the power trnasmission element, wherein the powertransmission element is movable by the power generator in apredetermined oscillation direction, and is formed from a vibrationalarm which is formed from a strip of flat material shaped to have aU-shaped section and has an open end and a closed free end, the open endbeing fixed to the holder and the closed free end being elasticallybendable in the oscillation direction and substantially rigid in otherdirections, and wherein one component of the permanent magnet part andthe coil part is fixed to the holder while another component of thepermanent magnet part and the coil part is fixed to the vibrational arm.2. The drive device according to claim 1, wherein the permanent magnetpart is a bell-shaped magnet fixed to the holder, and the coil part is aplunger coil fixed to the power transmission element.
 3. The drivedevice according to claim 1, wherein the coil part is electricallyconnected to a supply device containing an oscillation generator forgenerating a predetermined output frequency for excitation of the coilpart.
 4. The drive device according to claim 2, wherein the oscillationgenerator is adapted to generate an output frequency different from thenatural frequency of the power transmission element.
 5. The drive deviceaccording to claim 1, wherein the tool is a cutting tool of a microtome.6. The drive device according to claim 5, wherein the cutting tool is aceramic knife.
 7. A microtome equipped with a drive device according toclaim
 1. 8. The microtome according to claim 7, further comprising acontrol circuit for adjusting a predetermined oscillation amplitude andfrequency of a cutting tool of the microtome which contains the bendingsensor.
 9. The microtome according to claim 7, further comprising acontrol circuit for adjusting a predetermined oscillation amplitude orfrequency of the cutting tool which contains the bending sensor.
 10. Aprocess for generating oscillations with a vibrational device for a toolor a manipulator comprising a power transmission element which forms asupport for the tool or the manipulator, and a power generatorcomprising a permanent magnet part and a coil part, wherein one of theparts is fixed on a holder and another of the parts is fixed on thepower transmission element, wherein the power transmission element ismovable by the power generator in a predetermined oscillation directionand is formed from a vibrational arm which is formed from a strip offlat material shaped to have a U-shaped section and has an open end anda closed free end, the open end being fixed to the holder and, theclosed free end being elastically bendable in the oscillation directionand substantially rigid in other directions, and wherein one componentof the permanent magnet part and the coil part is fixed to the holderwhile another component of the permanent magnet part and the coil partis fixed to the vibrational arm, comprising: applying to the coil partof the power generator an excitation frequency different from thenatural frequency of the power transmission element, and exciting thecoil part by adjusting electrical parameters determined in a controlcircuit with a bending sensor.